A primary challenge this week sent a message to politicians nationwide about how much freedom they have to step outside party lines.

Leaders have always been second-guessed. These days, however, that tendency could cost some their jobs. William Howell, who has served as speaker of the Virginia House for a dozen years, has found that out. As an opponent of the Affordable Care Act and a former national chair of the American Legislative Exchange Council, he would appear to have his conservative credentials in order. Nevertheless, he faces a challenge from the right in the June 9 primary.

Susan Stimpson is attacking him for supporting a tax increase to pay for transportation. She’s backed by some of the same people who engineered last year’s biggest political upset, the primary defeat of Virginia Rep. Eric Cantor, who had been serving as the U.S. House majority leader.

Their voting records may suggest that both Howell and Cantor are solid conservatives, but that’s not enough to inoculate them from criticism, says Larry Sabato, a government professor at the University of Virginia. “It’s hard to serve as speaker and refuse to compromise,” he says. “In today’s GOP, it only takes one or two compromises on hot-button issues such as taxes or social issues to produce a primary challenge.”

Howell isn’t the only leader who has to worry. Various speakers such as Joe Straus in Texas and Beth Harwell in Tennessee have faced whisper campaigns or loud complaints that they aren’t conservative enough. In Nevada, Speaker John Hambrick survived an abortive recall campaign, brought on by loose talk around the capitol about a tax increase.

Leaders are still able to punish lawmakers who vote the wrong way by taking away committee assignments and parking spaces. But now they have to worry that if they step outside the party line themselves on a given issue, they could be attacked inside the chamber or back home. And, in the super PAC era, any plausible challenger can gin up funding for a real race. “As it always does, it seems to come back to campaign finance and money,” says Tim Storey, who tracks leadership issues for the National Conference of State Legislatures. “These low-turnout elections can be hijacked, and that’s a constant concern for leaders.”

Having seen what happened to Cantor, Howell is taking the threat he faces quite seriously. “To rest on your laurels and high office is to court disaster in today’s Republican politics,” Sabato says. “Howell gets it.” Whether he survives will say a lot to leaders around the country about how much freedom they have to move policy, even if it means casting a vote that won’t sell well in a primary.